As a standard of so called plug-and-play for a video display apparatus, there exists a standard called DDC (Display Data Channel). DDC is provided to exchange property information attributed to a video display apparatus (optimal resolution and the like) between a host (an apparatus which outputs a video signal) and the video display apparatus, so that the host side automatically performs settings corresponding to the properties of the video display apparatus.
In DDC, the property information attributed to the video display apparatus is exchanged in the form of formatted data called EDID (Extended Display Identification Data). Further, even in the state where power of the video display apparatus is being turned off, the EDID data can be transmitted from the video display apparatus to the host by supplying electric power from the host side to the video display apparatus. Hence, the EDID data is stored in a non-volatile memory such as an EEPROM in the video display apparatus so that the EDID data shall not vanish even in the state where the power is being turned off.
In the past, video output equipment that supports DDC was only a computer apparatus. As resolution of a RGB signal output from the computer apparatus, there exist such kinds as VGA, SVGA, XGA, and SXGA. Then, with respect to the resolution in a conventional video display apparatus that supports DDC, EDID data for the RGB signal having contents of, for example, “SVGA is optimal” was stored in a non-volatile memory (refer to, for example, FIG. 6 in page 2 of Japanese laid-open patent application No. H9-128330).
On the other hand, equipment that supports DDC has recently appeared also in an STB (Set Top Box) for DTV (Digital Television Broadcasting). As resolution of a television signal for the DTV (hereinafter, referred to a “DTV signal”), there exist such kinds as 1080I, 480I, 480P, and 720P (I and P represent distinction of a scanning method either Interlace or Progressive).
When a video display apparatus that supports DDC makes such STB perform settings in accordance with properties of the video display apparatus, with respect to the resolution, EDID data for a DTV signal having contents of, for example, “4801I is optimal” also needs to be stored in the non-volatile memory.
However, in DDC, EDID data items are each defined to be stored in a designated address inside a memory. FIG. 1 shows areas of the memory used by DDC. An area consisting of address 0-127 (byte) is defined as a standard area for storing the EDID data, and areas consisting of address 128-191, address 192-255, address 256-319, and address 320-383 are respectively defined as extended areas. Further, it is defined that the EDID data relating to the resolution should be stored in a predetermined address inside the standard area. Only one EDID data relating to the resolution (in case of the above described example, either the data of “SVGA is optimal” or the data of “480I is optimal”) can be stored in this predetermined address.
Moreover, although the EDID data for the RGB signal is normally stored only using the standard area, the EDID data for the DTV signal can not be stored only within the standard area and it is assumed that extended areas of address 128-191 and address 192-255 are to be used for storing. Further, in the predetermined address of the standard area, it is defined that data having contents of “read out EDID data from the extended area as well” is to be written when the EDID data is also stored in the extended area, and on the contrary, data having contents of “do not read out EDID data from the extended area” is to be written when the EDID data is not stored in the extended area. Therefore, except for a particular case in which EDID data for a RGB signal is stored also using the extended area, contents of data will be different in this predetermined address of the standard area when storing the EDID data for the DTV signal and when storing the EDID data for the RGB signal.
Due to the reason as described above, both the EDID data for the RGB signal and the EDID data for the DTV signal can not be stored in one non-volatile memory.
Accordingly, in order for settings in accordance with properties of a video display apparatus to be performed by both the computer apparatus and STB (to be performed on both the RGB signal and DTV signal), a method in which a non-volatile memory to store the EDID data for the RGB signal and a non-volatile memory to store the EDID data for the DTV signal are provided separately may be considered, for example.
FIG. 2 is a block diagram showing an example in which the above described method is realized. The EDID data for the RGB signal is stored in a DDC-supported EEPROM (a DDC-supported non-volatile memory will later be described) 31 and the EDID data for the DTV signal is stored in a DDC-supported EEPROM 32. A switch circuit 33 is provided for switching a computer apparatus and a STB connected to a video display apparatus to be connected to either the DDC-supported EEPROM 31 or the DDC-supported EEPROM 32.
When the computer apparatus is connected to the video display apparatus, a CPU 34 in the video display apparatus controls the switch circuit 33 based on an operation by a user or the like, so that the DDC-supported EEPROM 31 can be connected to the computer apparatus. Accordingly, since the EDID data for the RGB signal is exchanged between the computer apparatus and the video display apparatus, it is possible to make the computer apparatus perform settings for the RGB signal in accordance with properties of the video display apparatus.
On the other hand, when the STB is connected to the video display apparatus, the CPU 34 in the video display apparatus controls the switch circuit 33 based on the operation by the user or the like, so that the DDC-supported EEPROM 32 can be connected to the STB. Therefore, since the EDID data for the DTV signal is exchanged between the STB and the video display apparatus, it is also possible to make the STB perform settings for the DTV signal in accordance with properties of the video display apparatus.
However, when such method as illustrated in FIG. 2 is used, since the number of non-volatile memories increases in a video display apparatus, as a result the cost becomes high and increase in the area of a circuit board makes the whole video display apparatus difficult to be small-sized.
Particularly, although there are DDC-1 (in which information is transmitted uni-directionally from a video display apparatus to a host) and DDC-2 (in which bi-directional communications can be performed between the video display apparatus and the host) in DDC, DDC-1 and DDC-2 each have different communication protocols and the DDC-1 communication protocol is not supported by a non-volatile memory such as an ordinary EEPROM.
Therefore, in order to exchange EDID data with each of a host that supports DDC-1 and a host that supports DDC-2, it is necessary to store the EDID data in a particularly equipped non-volatile memory that supports both the DDC-1 communication protocol and DDC-2 communication protocol (refer to “a DDC-supported non-volatile memory” in this description. The DDC-supported EEPROM 31 and EEPROM 32 in FIG. 2 are also such DDC-supported non-volatile memories.).
This DDC-supported non-volatile memory is more expensive than an ordinary non-volatile memory. Therefore, such method as illustrated in FIG. 2 causes further increase in cost from this standpoint.
Also, there are at present only two kinds of DDC-supported image output equipment which are a computer apparatus outputting a RGB signal and a STB outputting a DTV signal. However, it is also predicted that in the future there will appear DDC-supported equipment that outputs a video signal other than the RGB signal and the DTV signal (for example, a digital component signal).
In such a case, if the method as illustrated in FIG. 2 is used, whenever a kind of video signal increases, the number of non-volatile memories needs to be increased, so that further increases in cost and in the area of the circuit board will inevitably occur.
In view of the above, the present invention is implemented with the object of enabling the host side to perform settings for plural kinds of video signals in accordance with properties of a video display apparatus and also, of facilitating reduction in cost and down-sizing, with respect to the video display apparatus that supports DDC.